The invention relates to an apparatus for taking a soil sample comprising a drill pipe, a first driving gear for introducing the drill pipe into the soil, a sampling bush which movably fits into the drill pipe and a second driving gear for introducing the sampling bush into the soil.
Such an apparatus is known in practice. Such an apparatus serves for taking soil samples to determine the physical and mechanical properties of the soil for the purpose of, for example, designing foundations, detecting soil pollution, examining the soil""s geological history of development, and the like. Such examination is carried out, among other things, by means of drilling holes, taking samples of the sediment in the bottom of the hole. Regularly increasing the depth of the drill hole, provides access to increasingly deeper soil strata each time taking samples in order to obtain a continuous soil profile geared to the requirements.
To obtain said samples, a distinction is made between two kinds of sediments: mineralized sediments and non-mineralized sediments. The invention intends to provide a sampling device suitable for taking a sample of non-mineralized sediments. Often samples of non-mineralized sediments are taken by driving a tube into the floor of the bore hole and subsequently extracting said tube with the obtained sample from the soil. However, the possibilities of driving a tube into the ground in a large variety of sediment types in a manner such as to allow the core to be recovered relatively intact, are limited.
Among the prior art methods of taking a soil sample in non-mineralized sediments are the following.
The drill hole may be drilled by rotating a steel pipe provided at its bottom end with a cutting shoe, whereby a compressive force is exerted on the cutting shoe for the cutting process. During rotation liquid is pumped down through the pipe taking away the cut material via the annular space between the drill pipe and the wall of the drilled hole. The cutting shoe at the lower end of the drill pipe has a central opening (or can be opened by removing a central part of the cutting shoe to facilitate the sampling process) such as to allow sampling equipment access to the sediment below the level of the cutting shoe. For application on land, the axial line of the drill pipe""s interior is usually limited to 75 to 200 mm, and at sea to 75 to 100 mm. As a result, sampling apparatuses may only have a small diameter. The use of larger axial lines considerably increases the costs because it involves heavier drilling machines, more space and finally, at sea, the required vessels have to be of larger dimensions. Soil samples are taken by pushing or driving an open tube (sampling bush) into the floor of the hole by one of the following manners of operation.
In a first known method, the sampling bush is connected with a series of extension rods, while the surface of the rods are struck in order to drive the rods into the ground, see for example U.S. Pat. No. 5,211,248. This technique is also applied with subaqueous soils, the hammer operating inside a sleeve to guarantee the functioning of the hammer; see, for example WO 94/23181. With this manner of operation a variety of machines may be employed which are based on, for example, high-frequency and -efficiency hydraulic or pneumatic hammers. This technique is limited to a depth at which the energy can still be transmitted effectively via the extension rods between the surface and the bottom of the hole to the sampling bush. In practice this depth is several tens of meters in connection with energy reflections at the joints between individual rods, the limited rigidity of the rods, their susceptibility to bending, etc.
For greater depth, a second known technique reports the taking of samples using a very simple method of ramming, namely by using a falling weight that is hoisted up and down with the aid of a winch at the surface, and by letting this weight fall on an anvil fastened at the top side of the sampling bush.
The mass of the falling weight is limited by the small diameter of the drill pipe. Weights in the order of 50 to 100 kg are commonly used. The falling velocity is determined by the earth""s gravitational force on the mass, reduced by retarding influences such as the resistance the falling weight experiences from the drilling liquid. The liquid under the falling weight has to be displaced and has to flow upward past the falling weight; this resistance is considerable, as the falling weight has to move in a very narrow space. The force required to counter the mass inertia of the winch drum and to pull the cable off the winch, and the resistance experienced by the winch cable from the drilling liquid, also play a role. Practice has shown that in very undeep drill holes considerable energy per stroke may be delivered. However, this greatly decreases with the length of the winch cable and consequently with the depth of the drill hole and, when drilling at sea, the depth of the drill hole increased with the distance of the ship to the sea floor. At a depth of 150 to 250 metres, depending on the mass used for the falling weight and the winch used, the energy is decreased to such an extent that by this manner of operation it is only possible to take samples of soft sediments.
Another aspect of this method when operating at sea relates to the effectiveness of the stroke force. Due to the rolling movement of the vessel the hoisting height of the falling weight and thus the falling height of the falling weight varies. As the available hoisting height in connection with the total allowable length of the apparatus is limited to 1 to 2 metres, it frequently happens when hoisting the falling weight, that the upper check of the hoisting height is reached and resulting in an upward stroke being made. This upward stroke has a very adverse effect on the quality of the sample to be taken. Another occurrence when using this technique at sea is that the precise depth of penetration at any moment is only known by approximation, so that after having been completely filled with sediment, it frequently happens that the sampling bush is driven even deeper into the ground, which also has a very adverse effect on the sample already taken.
Another disadvantage of this method is that the stroke frequency is very low due to the fact that the stroke force is delivered by hoisting the weight at the surface by means of a winch and waiting each time long enough to be certain that the falling weight has reached the check. In practice only one stroke per 5 to 15 seconds can be delivered.
In a third known technique samples are taken by driving the sampling bush into the sediment by means of a hydraulic jack. To this end the jack is temporarily anchored in the lower end of the drill pipe and driven by a liquid pumped down through a tube. Due to the small diameter it is possible with the usual liquid pressures to realize a compressive force of 50 to 100 kN.
In an alternative method of this known technique the drilling liquid is used as pressure medium. In this technique the drill pipe is sealed off at the lower end by the sampling apparatus, and the drilling liquid is compressed by means of a pump at the surface, for driving the hydraulic pressure device. In this method it is preferred that the pressure device be unmovable in relation to the floor of the hole. Therefore, at sea the drilling pipe in which the sampling apparatus is anchored, has to be vertically stabilized independently of the rolling movement of the vessel. Also, sufficient reactive force has to be supplied. To this end a scaffolding of adequate substance is lowered onto the sea bed and during sampling the drill pipe is clamped in this scaffolding. Simultaneously, the upper end of the drill pipe is kept in communication with the hoisting device aboard the vessel via a swell compensator.
One aspect of the quasi-statical driving of a sampling bush into the sediment relates to the friction the sampling bush applies to the entering sediment. This friction must be limited so as not to disturb the sample too much. In practice this means that the cutting depth is limited to 0.5 to 1.5 metres, depending on the type of sediment. In practice, the force that can be attained usually allows sufficiently long samples to be taken in solid clays and dense sands. In very hard clays and very dense sands, however, only slight penetration is realized.
From GB-A-2.142.364 an appartus is known for taking a soil sample comprising a drill pipe, a first driving gear for introducing the drill pipe into the soil, a sampling device comprising a sampling bush which movably fits into the drill pipe, and a hammer device, wherein the hammer device is movable in the drill pipe, and wherein on top of the sampling bush an anvil is provided whereby the hammer device is of the liquid-driven kind and serves as a second driving gear for introducing the sampling bush into the soil.
The sampling device of this known apparatus provides the advantage that it offers a high stroke frequency for driving the sampling bush in. As a result, driving the sampling bushes into clay-like soils, generates an elevated water tension in the sediment, which can greatly reduce the penetration resistance experienced by the sampling bush, thereby increasing the effectiveness of the apparatus. The fact that the hammer device according to the invention is provided directly above the sampling bush (xe2x80x9cdown the holexe2x80x9d), provides a very efficient and effective energy transmission which is independent of the depth at which sampling is to take place. Moreover, this apparatus is well suited for taking long samples.
The apparatus for taking a soil sample according to the invention is characterized in that the hammer device is provided with an internally extending sealable feed-through channel which is opened when a hammer element movable in the hammer device is resting on the anvil, and closed when the movable hammer element is at a distal position in relation to the anvil. In this manner the pressure that is built up above the hammer device simultaneously acts as drive force for said hammer device.
Conveniently, the hammer device is externally provided with a sealing member working together with the inside of the drill pipe, and the drill pipe can be sealed at its top. This allows a pressure to be built up within the space defined by the top of the hammer device and the drill pipe sealed at its top, which activates the hammer device. In addition, the movability of the hammer device in the drill pipe allows this pressure to boost the driving in of the sampling bush into the sediment.
Advantageously, the drill pipe is provided at its inside at a preadjusted height, with a grove for the interruption of the effect of the sealing member. When the sampling bush has reached the desired depth of penetration into the sediment, this provision allows the pressure above the hammer device to fall out, so that the sampling bush is fixed at its depth of penetration then reached.
It is furthermore useful that the feed-through channel of the hammer device runs through the hammer element, and that said feed-through channel comprises a valve which, when the hammer element is in the distal position, rests on said hammer element, thereby closing off the feed-through channel, and that inside the hammer device tappets are provided-on which the valve rests when the hammer member rests on the anvil, whereby then the feed-through channel is opened up.
In yet another aspect of the invention the apparatus is characterized in that the sampling bush, preferably at its top side, has one or more outwardly extendable projections, and that the drill pipe, at its lower end has an inwardly directed narrowing. After the sampling bush has completed its penetration into the sediment, said sampling bush can then be removed by simply pulling it out of the bottom of the drill hole simultaneously with the lifting of the drill pipe.
Preferably also the hammer device is at its upper end provided with a fish tail to allow said hammer device to be removed from the drill hole with the aid of a fishing apparatus.
In yet another aspect of the invention the sampling bush is embodied with an integrated deceleration element and above said deceleration element the sampling bush is provided with one or more outlet openings. This achieves that the liquid peak pressure in the sampling bush developing as it is being driven in is limited in said sampling bush, but above the sediment. The effect of this peak pressure is such that it reduces the drive-in efficiency of the sampling bush. In order to limit the peak pressure, the deceleration element ensures that during the driving in of the sampling bush, the liquid above the sediment in the sampling bush can leave the same as quickly as possible through the outlet openings.
In yet another aspect of the invention, the sampling bush is provided at its top side with a one-way valve located below the outlet openings in the sampling bush, which valve closes off when an underpressure exists in the sampling bush. This ensures that during the removal of the sampling bush from the sediment, the extracted sediment sample will remain as much as possible intact, due to the fact that during retraction of the sampling bush, the valve causes the creation of an underpressure above the sediment sample.
Usefully, the one-way valve is embodied as a heavy ball element resting on a seating. This effectively combines the above-discussed role of the valve with the previously-mentioned measure of the deceleration element limiting the peak pressure.
In an alternative embodiment the one-way valve is embodied as a ball element resting on a seating, and the deceleration element is coupled with the ball element. Preferably, the deceleration element defines a gas-filled chamber.
Another embodiment of the apparatus is characterized in that it is provided with a rod that can be fixed in the drill pipe and that extends through the sampling device, and which at the lower side of the sampling bush is provided with a piston element with a liquid-proof seal, while the sampling bush above the piston element is provided with openings. When the sampling bush accelerates downward, the piston element remains in place because the rod is fixed in relation to the drill pipe, and the liquid above the piston element is driven out of the sampling bush via the openings, so that the peak pressure has no effect on the entering sediment.
A possible embodiment of the apparatus according to the invention is characterized in that the sampling bush and the hammer device are embodied such as to be separate and separable.